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Binding of Shigella to rat and human intestinal mucin
R Rajkumar1, H Devaraj, S Niranjali
1Department of Biochemistry, University of Madras, Chennai, India.
Abstract:
Invasion of epithelial cells by Shigella is an early step in their pathogenesis. Adherence is generally presumed to be a prerequisite for invasion. This study examined the possibility of intestinal mucins serving as initial binding sites for clinical isolates of S. boydii and S. sonnei. The interactions of Shigella with rat and human small intestinal and colonic mucin were investigated. In solid phase binding assays, [35S] labelled Shigella did not show any preferential binding to rat/human small intestinal mucin or to rat colonic mucin. On the other hand, Shigella bound specifically to human colonic mucin in a concentration-dependent manner. This specific binding to human colonic mucin was not by weak hydrophobic interactions and could not be attributed to the presence of contaminating glycolipids in the mucin preparation. The human colonic mucin receptor was sensitive to periodate treatment suggesting the involvement of the carbohydrate portion of the mucin. Reduction and alkylation of mucin enhanced adherence probably by exposing buried binding sites. The monosaccharides present in mucins were ineffective as hapten inhibitors as was the lectin wheat germ agglutinin suggesting that the mucin receptor is a more complex one. This study identifies, for the first time, the presence of a specific Shigella-binding site on the carbohydrate portion of human colonic mucin, which is not present in rat colonic mucin or in rat/human small intestinal mucin.
Insights
Shigella bacteria specifically bind to human colonic mucins, a key step for invasion. This interaction involves the carbohydrate portion of mucin, offering a novel target for therapeutic interventions against Shigella infections.
Area of Science:
- Microbiology and Immunology
- Gastroenterology
Background:
- Epithelial cell invasion by Shigella is a critical early event in pathogenesis.
- Bacterial adherence to host cells is typically considered a prerequisite for invasion.
Purpose of the Study:
- To investigate intestinal mucins as potential initial binding sites for clinical Shigella isolates (S. boydii and S. sonnei).
- To characterize the specific interactions between Shigella and human/rat small intestinal and colonic mucins.
Main Methods:
- Solid-phase binding assays using [35S]-labeled Shigella and purified rat/human intestinal and colonic mucins.
- Investigation of binding characteristics, including concentration-dependence, hydrophobic interactions, and glycolipid contamination.
- Assessment of mucin receptor sensitivity to periodate treatment, reduction, and alkylation.
Main Results:
- Shigella exhibited no preferential binding to rat/human small intestinal mucin or rat colonic mucin.
- A specific, concentration-dependent binding of Shigella to human colonic mucin was observed.
- The binding site on human colonic mucin involved its carbohydrate portion and was not due to hydrophobic interactions or glycolipid contamination.
Conclusions:
- This study identifies a specific Shigella-binding site on the carbohydrate component of human colonic mucin.
- This binding site is absent in rat colonic mucin and rat/human small intestinal mucins.
- The findings suggest a novel mechanism for Shigella adherence and potential invasion via human colonic mucins.